1. Field of the Invention
The present invention relates to a touch sensing circuit, and more particularly, to a touch sensing circuit which can sense whether or not a touch is made on the touch screen panel by detecting a difference in variation of coupling capacitances between mutually adjacent driving electrodes when a finger is touched on a touch screen panel.
2. Description of the Related Art
With miniaturization of electronic devices, a touch screen panel (TSP) is widely used as an input device. A TSP is provided on the rear side thereof with a display unit, an image or the like outputted from the display unit is transmitted through the TSP and then is shown to the user, and a corresponding electronic device performs a user's instruction when the user touches the TSP and applies the instruction while seeing the image or the like.
Such a TSP shows a tendency to use a capacitance scheme in order to detect an input position on the TSP. The capacitance scheme is to generate a minute variation in instantaneous current through capacitance when the user touches his/her finger to a dielectric film formed on electrodes of a TSP, and to enable a touched position to be detected from the minute change.
Meanwhile, according to such a capacitance type touch screen panel (TSP), even when the user uses the TSP in a multi-touch manner as touching a plurality of points through a plurality of fingers at the same time, the plurality of points can be recognized at the same time.
FIG. 1 is a view illustrating the configuration of a conventional capacitance type touch sensing device.
Referring to FIG. 1, a capacitance type touch sensing device 100 includes a touch screen panel 110 and a detection means 120. The touch screen panel 110 includes a plurality of driving electrodes 111a to 111n, which are extended in a row direction and are connected to a plurality of sensing channels 112a to 112n, and a plurality of receiving electrodes 113a to 113n, which are extended in a column direction and are connected to a plurality of sensing channels 114a to 114n. 
The plurality of driving electrodes 111a to 111n and the plurality of receiving electrodes 113a to 113n are arranged on mutually different planes, and include parasitic impedances, such as parasitic resistance Rp and parasitic capacitance Cp1. Also, in each node where the plurality of driving electrodes 111a to 111n and the plurality of receiving electrodes 113a to 113n cross each other, a coupling capacitance Cc is formed. Therefore, the plurality of driving electrodes 111a to 111n, the coupling capacitance Cc, and the plurality of receiving electrodes 113a to 113n form a detection path where a variation in coupling capacitance is detected.
In this case, when one of the plurality of driving electrodes 111a to 111n is touched by the user, a variation in coupling capacitance Cc between the touched driving electrode and a receiving electrode which crosses the touched driving electrode is generated, so that it is possible to determine whether or not the touch screen panel 110 is touched by sensing the variation through the detection means 120.
FIG. 2 is a view illustrating the structure of a touch screen panel.
Generally, touch screen panels (TSPs) are classified into add-on type and on-cell type according to forms in which display panels are installed.
In FIG. 2, (a) is a view illustrating the configuration of an add-on type touch screen panel, and (b) is a view illustrating the configuration of an on-cell type touch screen panel.
As shown in (a) of FIG. 2, an add-on type touch screen panel (TSP) has a structure in which a TFT substrate 11, a color filter substrate 12, an insulating layer 13, a touch screen substrate 14, and a tempered glass substrate 15 are formed in regular sequence.
In contrast, as shown in (b) of FIG. 2, an on-cell type touch screen panel (TSP) has a structure in which a touch screen substrate 14 is formed directly on top of a color filter substrate 12, without an insulating layer.
The structure of the on-cell type touch screen panel (TSP) has an advantage in that the entire thickness of the panel can be reduced. However, as compared with the add-on type touch screen panel (TSP), the on-cell type touch screen panel (TSP) is vulnerable to display noise and peak noise because the touch screen substrate 14 gets near to the TFT substrate 11, on which a display driving circuit is formed.
As shown in (c) of FIG. 2, various parasitic capacitances CS, CG, and CCOM, are generated between the driving electrodes of the touch screen substrate 14 and the source line, gate line, and intermediate voltage lines of the TFT substrate 11. However, the on-cell type touch screen panel (TSP) has a problem in that the various parasitic capacitances CS, CG, and CCOM further increase in magnitude because the touch screen substrate 14 and the TFT substrate 11 get near to each other.